Transmitting electronic mail (e-mail) messages is one of the major functions served by the Internet. With its phenomenal growth in the late 1990s, the Internet has replaced several proprietary e-mail messaging systems and become the ubiquitous global network for e-mail messaging.
Due to the cost and technical complexity involved in hosting an e-mail server on the Internet, many small business entities and individual users do not host their own Internet e-mail servers. Instead, they use Internet mail servers provided by their Internet Service Providers (ISPs) to transmit and receive e-mail messages to and from the Internet. In such an arrangement, Internet e-mail messages destined for users on the local area network (LAN) of a business entity are first routed through the Internet to the ISP's Internet mail server and held in a mailbox for that business entity. A mail server of the local area network then uses a mail connector software module to connect to the Internet mail server of the ISP and download the e-mail messages from the mailbox at the Internet mail server, and distributes the downloaded messages to their intended recipients.
Currently, most mail servers implement the Post Office Protocol Version 3 (POP3) for handling the exchange of e-mail messages, and the mail connector used for downloading e-mail messages from the Internet mail server is programmed to operate according to the POP3 requirements. Other e-mail access protocols have been proposed, however, with the intent to provide enhanced e-mail messaging functionality. One example is the Web Distributed Authoring and Versioning (Web DAV) protocol. Those e-mail access protocols not only define different e-mail access operations but also use different message formats. For instance, the POP3 requires e-mail messages to be in the Internet Message Format (IMF) defined in RFC 822 of the Internet Engineering Task Force (IETF), while the Web DAV protocol requires the e-mail messages to be in the Extensible Markup Language (XML) format.
Due to the importance of Internet e-mail messaging, more e-mail access protocols and message formats will likely be proposed and implemented in the future. It is expected that a local area network may have e-mail accounts with multiple Internet mail servers that support different e-mail access protocols. Thus, the mail connector software has to have the ability to access e-mail messages at the Internet mail servers according to the different protocols and the ability to handle different message formats. From the viewpoint of a software developer, however, it is desirable to minimize the amount of re-programming work that has to done to modify the mail connector software or the like to provide support for new e-mail access protocols and message formats. Accordingly, there is a need for a software module for use by a local mail server to access e-mail messages at Internet mail servers that can be easily extended to support various e-mail access protocols and message formats.